During the past year new Ia specificities were identified in haplotypes H-2p, H-2r, H-2v, H-2u and H2j. The mapping and the tissue expression of these specificities are currently underway. The tissue expression of Ia antigens was extended to include non-lymphoid cells such as peritoneal neutrophils and the gut-associated Peyer's Patch cells. Both of these cells expressed Ia antigens associated with the I-A and I-E subregion gene products. Further, several Ia ion tumor lines were also identified. Chemical characterization of these antigens on these tissue are currently underway. During the past year Ia molecules associated with the I-E subregion of silent haplotypes H-2s, H-2t, H-2b and H-2q were identified immunochemically using heteroantisera made against NP-40 solubilized glycoproteins. This antisera identified a non-polymorphic Ia gene product which was present in all mouse strains. During the past year several new monoregional and monospecific anti-Ia reagents were produced for serological and chemical studies as well as functional analysis of Ia antigens. Studies are underway to determine whether Ia antigen positive epidermal cells and Peyer's Patches can function as antigen presenting cells. Further, experiments are also underway to determine whether one of the functions of Ia antigens may be presenting the antigens to the T cells.